mineral

Tumbled howlite (likely)

Howlite, Ca₂B₅SiO₉(OH)₅

AI-generated identification · may be incorrect

White to pale gray, opaque, with distinctive dark gray spiderweb veining; vitreous to dull luster and uneven fracture. Mohs hardness 3.5, monoclinic crystal system, specific gravity about 2.5–2.6; the pictured piece is polished/tumbled.

Identified August 30, 2026More mineral →

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Physical properties

Formation & geological history

A borate mineral formed in evaporite-related clay deposits, commonly in arid sedimentary basins; notable deposits occur in California and Nova Scotia. It formed geologically recently compared with most bedrock, with no single age assignable to specimens.

Uses & applications

Commonly sold as a cabochon, tumbled stone, carving material, and imitation turquoise when dyed; it has limited industrial use.

Geological facts

Howlite is porous and readily accepts dye, so blue “turquoise howlite” is widespread. Its webbing can resemble turquoise or marble, but its low hardness helps distinguish it.

Field identification & locations

Identify by its low hardness, chalky white-gray body, irregular dark veins, and light weight; it can be scratched by a steel knife. Similar-looking magnesite and marble require testing or laboratory analysis.